why did other Indians tribes join with Cortes against the Aztecs?

Answer 1

Because the Aztecs had many enemies. The Aztecs were the ruling tribe and many other tribes were conquered by them or enslaved by them. So there were many other tribes willing to help take them down.

Same thing happened with Africans, many other tribes helped the European capture slaves by turning over their enemies to them. Of course only SOME slaves were captured that way.

Answer 2

Because the Aztecs used them as human sacrifices and slaves.

Answer 3

They got tired of having their people sacrificed on Aztec pyramids, it tends to make enemies...trust me.